Aiming at the problems of large mass and difficulty in passing in hilly and mountainous fields of the current 4YZLP-2C crawler corn combine harvester, the lightweight design of the frame was carried out. Solid works were used to conduct the parametric model of the frame, and the finite element model was was established based on the parametric model of the frame. Modal analysis was carried out through the finite element model, and the validity of the finite element model was verified by the modal test of the frame. The mechanical properties of the frame were analyzed to obtain the results of stress and deformation. Based on the relative sensitivity analysis, the thickness of 17 parts of the frame was selected as the design variable, to establish the surrogate model by Latin hypercube experimental design and Krieger method. By taking the maximum equivalent force under the field obstacle crossing condition, the maximum total deformation under the full load bending condition and the maximum total deformation under the bending condition as the constraints, and the frame quality and the minimum total deformation under the field obstacle crossing condition as the optimization goals. the multi-objective lightweight design is carried out through the MOGA algorithm. After the lightweight of the frame, the weight of the frame is reduced by 31.56 kg compared with that before optimization, and the maximum deformation under obstacle crossing conditions is also reduced by 0.33 mm.